Glad it's useful to some.
If you want to know whether or not it will work with your particular model or hmp, my advice is to copy and paste the grass stuff into your terrain action. The grass script is at the top of the terrain action. I kept it separate from JCLs script. Then follow the instructions and let the grass script do its thing.

Although I don't like rapidshare myself, I can't just post the script here. You'll need the grass models too. You may need the terrain and colormap to see how the script works, and adapt it to your game. If anyone can host the file, feel free to do so. It's over 5MB.

I see no reason why it should not work with 6.3, but since I don't have it, I make no guarantees.